Guy's,
Was beginning to wonder whether any of the contributors to this thread had any experience of CDA's in the real world until Scrogg's and G W-H's comments. The idea of idle thrust descents from cruise level to 1000' AGL within busy UK/European airspace is totally unrealistic, and rather ignorant (although that's not to say it cant be done in places!)
CDA's seem to be the flavour of the month at the moment in terms of environmental issues, or to put it simply, reducing noise. Definitions of CDA's that i've seen are similar to that suggested by G W-H - they mention something with regards to the pilot, after leaving a given fix/level, should judge his rate of descent such as to arrive at final approach without recourse to level flight.
Although I consider it good handling & airmanship to practice CDA's on every approach, in many cases it is just not possible. Aerodromes that specify such approaches are generally well set up to support them - regular estimates of track miles remaining are provided on leaving the holding fix/STAR end waypoint, all of which makes the execution somewhat simpler. Elsewhere, the task is a bit more complex.
In terms of the automatics, I can only say that the FMS on the scarebuses that I fly are not really capable of CDA approaches. The boxes have a nasty habit of prescribing level-off's in their profiles to allow deceleration (e.g. 250kts to min clean speed etc). Subsequent flight in managed descent (Airbus V-NAV) results in these level-off's. Thus, invariably, CDA's are flown in Speed - V/S modes, or if one is feeling particularly sporty, via manual flight.
I also totally agree with alf5071h's comments with regard's to NPA's - they should all be flown without level-off, where possible. However, i have always referred to such approaches as "balanced, stabilised approaches", not CDA's. Would be interested to hear other people’s comments!
Regards,
Cuban_8